In this thesis, a model has been developed to analyze the behavior of wave energy converter arrays in the frequency domain. This development serves the purpose of establishing an in-house model tool for array modelling for CorPower Ocean. A literature review has been conducted to compare various modelling approaches and prior studies on different configurations of wave energy converter arrays have been examined. The literature review is followed by theory that includes linear wave theory and the equation of motion. Following this, the model is introduced, accompanied by behavior validation in comparison to similar models. The selected case studies for this thesis are divided into two parts. Firstly, the investigation of different layout configurations with 16 Wave Energy Converters: 1) Circular configuration, 2) Double Circular configuration, 3) Double Row configuration (2x8), 4) Square Grid configuration (4x4), and 5) Randomized layout. The second chosen study case involves investigating layout 3) Double Row configuration (2x8) with four different distances between each Wave Energy Converter, 50, 100, 150, and 200 meters. The results demonstrate the presence of interactions within the wave energy converter arrays. The Double row layout exhibits the largest power outputs but power drops at certain waveperiods were also observed. Additionally, the results of different distances between the Wave Energy Converters demonstrate that larger spacings result in reduced interactions.

The ability to control the trajectory and understanding the atmospheric effects on the flight performance of a scientific high altitude balloon has long been an aspiring ambition. This thesis work analyses the thermal and optical environments at float using the simulation software, ANSYS FLUENT. The objectives for this thesis were to evaluate how the solar angle, sunshine factor and the ground emissivity altered the altitude for the balloon during floating condition in Steady-state simulations. A transient simulation was conducted to evaluate the diurnal cycle effects on the altitude of the balloon. The understanding of how the parameters influence the altitude will make it possible to autonomously route the balloon to desired altitudes where you have a favorable wind direction. Performing steady-state simulations showcased the significance of certain parameters. Different solar angles greatly influenced the temperature gradient on the balloon and hence a larger lifting force acted on the balloon when the sun was at its highest point. Varying the cloudiness mostly affected the maximum temperature distribution and did not affect the minimum temperature distribution. The steady-state simulations also indicated a limited but noticeable dependence on the ground emissivity. From the transient simulations it was further enhanced how great of influence the solar angle have, which was illustrated by running diurnal cycles. It was also apparent that there are great differences depending on the seasons. For future applications, it would be of interest to investigate the effects caused by wind velocities in the steady-state case. A comparative analytic solution should be performed in order to validate the simulation results.

The manufacturing process for the core of an RIP bushing was studied. Simulations of a test model was performed, due to the non-linear nature of the fluid filling process. Varying of governing parameters in the model, that could realistically be varied, was carried out and their affect was observed. The model was then compared to real measurements to view its practical reliability. Proposals to optimize the filling speed of the process in order to avoid the creation of bubbles was discussed and conducting it would be the next step for further research of the subject.

<p>Rheumatoid arthritis (RA) is a systemic disease that can affect the nervous system, lungs, heart, skin, reticuloendothelium and joints. Currently, the gold-standard measurement for tracking the progression of the disease involves a semi-quantitative assessment of bone erosion, bone marrow edema and synovitis, as seen in magnetic resonance (MR) images, by a musculoskeletal radiologist. The work presented in this thesis identifies how computer automation can be used to quantify bone erosion volumes in MR images without a radiologists' expert and time consuming intervention. A new semi-automated hybrid segmentation algorithm that combines two established techniques: region growing and level-set segmentation, is described and evaluated for use in a clinical setting. A total of 40 participants with RA were scanned using a 1-Tesla peripheral MR scanner. Eight of the participant scans were used to train the algorithm with the remaining used to determine the accuracy, precision, and speed of the technique. The reproducibility of the hybrid algorithm and that of manual segmentation were defined in terms of intra-class correlation coefficients (ICCs). Both techniques were equally precise with ICC values greater than 0.9. According to a least squares fit between erosion volumes obtained by the hybrid algorithm with those obtained from manual tracings drawn by a radiologist, the former was found to be highly accurate ( m=1.030, b=1.385: r-squared=0.923). The hybrid algorithm was significantly faster than manual segmentation, which took two to four times longer to complete. In conclusion, computer automation shows promise as a means to quantitatively assess bone erosion volumes. The new hybrid segmentation algorithm described in this thesis could be used in a clinical setting to track the progression of RA and to evaluate the effectiveness of treatment.</p> / Doctor of Philosophy (PhD)

This master’s thesis project investigates the utilization of a low-cost hyperspectral (HS) imaging rig to identify and classify drought stress in pine plants. Drought stress is a widespread environmental challenge affecting global forestry, requiring more resources as the industry grows and global warming rises. This provokes a need for affordable, and efficient monitoring methods. HS imaging, with its ability to capture a wide range of spectral information, offers promising methods for quick and precise measurements of plant stress. The project methodology is comprised of redesigning an existing HS imaging rig, with the camera employing push-broom technology, to yield precise and consistent HS images. This involved exploring the camera’s spectral range, designing components to ensure consistent artificial lighting using blackbody radiation sources, and calibrating the HS camera for focal depth and aberrations like smile and keystone. Two experiments were conducted to obtain the data for pine stress detection, first for two binary categories: Control, and 100% Drought, and later introducing a third semi-drought category in the second experiment. The data analysis encompassed preprocessing the HS images to correct the lighting intensity distributions and normalization of pixel values. Accompanied by filtering, resampling spectral data, and feature extraction facilitating consistent drought identification, and data management. To identify stress patterns in pine plants and temporal decay rates, methods such as spectral reflectance analysis, various vegetation indices (VI), and statistical learning techniques like discriminant analysis and logistic regression were evaluated for distinguishing between stressed and healthy plants. The results demonstrate the accuracy of the HS imaging rig in measuring spectral reflectances from plants, capturing changes between 550 − 670 nm in the visible spectrum and 750 − 890 nm in the near-infrared (NIR) spectrum due to increasing stress affecting chlorophyll levels. Both well-established VIs and empirically designed indices indicate reliable early detection. Comparing multiple VIs to statistical learning models shows similar performances in binary classification tasks. Feature selection methods using correlation matrices, and L1 penalty for logistic regression support stress effects visible in the data, paving the way for cost-effective strategies in sustainable forestry management.

Magnetic resonance imaging (MRI) utilizes the magnetic properties of tissues to generate image-forming signals. MRI has exquisite soft-tissue contrast and since tumors are mainly soft-tissues, it offers improved delineation of the target volume and nearby organs at risk. The proposed Magnetic Resonance-only Radiotherapy (MR-only RT) work flow allows for the use of MRI as the sole imaging modality in the radiotherapy (RT) treatment planning of cancer. There are, however, issues with geometric distortions inherent with MR image acquisition processes. These distortions result from imperfections in the main magnetic field, nonlinear gradients, as well as field disturbances introduced by the imaged object. In this thesis, we quantified the effect of system related and patient-induced susceptibility geometric distortions on dose distributions for prostate as well as head and neck cancers. Methods to mitigate these distortions were also studied. In Study I, mean worst system related residual distortions of 3.19, 2.52 and 2.08 mm at bandwidths (BW) of 122, 244 and 488 Hz/pixel up to a radial distance of 25 cm from a 3T PET/MR scanner was measured with a large field of view (FoV) phantom. Subsequently, we estimated maximum shifts of 5.8, 2.9 and 1.5 mm due to patient-induced susceptibility distortions. VMAT-optimized treatment plans initially performed on distorted CT (dCT) images and recalculated on real CT datasets resulted in a dose difference of less than 0.5%.  The magnetic susceptibility differences at tissue-metallic,-air and -bone interfaces result in local B0 magnetic field inhomogeneities. The distortion shifts caused by these field inhomogeneities can be reduced by shimming.  Study II aimed to investigate the use of shimming to improve the homogeneity of local  B0 magnetic field which will be beneficial for radiotherapy applications. A shimming simulation based on spherical harmonics modeling was developed. The spinal cord, an organ at risk is surrounded by bone and in close proximity to the lungs may have high susceptibility differences. In this region, mean pixel shifts caused by local B0 field inhomogeneities were reduced from 3.47±1.22 mm to 1.35±0.44 mm and 0.99±0.30 mm using first and second order shimming respectively. This was for a bandwidth of 122 Hz/pixel and an in-plane voxel size of 1×1 mm2.  Also examined in Study II as in Study I was the dosimetric effect of geometric distortions on 21 Head and Neck cancer treatment plans. The dose difference in D50 at the PTV between distorted CT and real CT plans was less than 1.0%. In conclusion, the effect of MR geometric distortions on dose plans was small. Generally, we found patient-induced susceptibility distortions were larger compared with residual system distortions at all delineated structures except the external contour. This information will be relevant when setting margins for treatment volumes and organs at risk.   The current practice of characterizing MR geometric distortions utilizing spatial accuracy phantoms alone may not be enough for an MR-only radiotherapy workflow. Therefore, measures to mitigate patient-induced susceptibility effects in clinical practice such as patient-specific correction algorithms are needed to complement existing distortion reduction methods such as high acquisition bandwidth and shimming.

In this project a qutrit tripod system is studied to implement quantum gates using non-Abelian geometric phases, allowing for holonomic quantum computation which in turn results in more robust computations. First, a general foundation of the theory is presented. This includes the relevant theory of matrices in Hilbert space, as well as theory of the quantum mechanics used in the report. The method is then described in depth, showing how the pulse area is fixed. Using properties of the Hamiltonian as well as the time-evolution operator of the tripod system the computational subspace can be derived. These findings are combined to show how the computational subspace evolves in time, resulting in the unitary matrix used to form quantum gates. Using educated guesses to find the necessary parameters or utilizing iterative methods to find the parameters are the two main approaches used for constructing the considered gates. Three of the suggested quantum gates are successfully implemented through educated guesses, namely X, T and Z using an angle parametrization of the phase and amplitude of the pulses. The last desired gate is the Hadamard-gate, but the implementation of said gate required numerical approximation. The reasons as to why this is the case, are later discussed.

No description available.

Energy resolution characteristics of silicon surface barrier detector signals amplified by different preamplifiers and spectroscopic amplifiers have been studied. The characterization has been done using alpha particles from an 241Am source and spontaneous fission fragments from two Cf sources. The alpha and spontaneous fission activities of the sources have been measured and the isotopic compositions, ages, and initial activities of the two Cf sources have been calculated using the results from the activity measurements. 82.3% and 82.5% of the spontaneous fission activity of the two sources is found to originate from 252Cf. Heavy ion detection properties of two Si detector setups have been determined by measuring spontaneous fission fragments from one of the Cf sources in coincidence. The mass distribution of fission fragments is derived from the pulse spectra of the coincidence measurements. The conditions for future time resolution measurements have been established. Inquiries on commercially available ultra-thin Si detectors have been made. The purpose is to upgrade detector telescopes to lower the energy threshold of ΔE-ΔE-E identification of particles from neutroninduced nuclear reactions. Three manufacturers of Si detectors with thickness 20-25 µm and active area around 450 mm2 have been listed together with properties of the three offered detectors.

This thesis uses theoretical studies, and numerical simulations to provide results of the experimental reach to detect the QCD axion as dark matter in a Non-standard cosmological background. Assuming that the QCD axion constitutes the full CDM abundance of the universe, this thesis elaborates on its potential detection from experimental setups for the mass window of the axion. The set of results that is obtained here are the relic CDM energy density of axions produced by the vacuum realignment mechanism and the CDM energy density of axions produced from the decay of a network of cosmic strings. This thesis provides results regarding the possibility to detect a primordial gravitational wave relic, which is possible within some favorable cosmological scenarios for the background.